# Multispectral Holographic Intensity and Phase Imaging of Semitransparent Ultrathin Films

## TL;DR

A new optical imaging method is introduced to study thin, semitransparent materials by capturing both light intensity and phase.

## Contribution

The novel method combines intensity and phase imaging to determine optical properties like complex refractive indices of ultrathin films.

## Key findings

- The LIM technique successfully characterized CuO-seeded gold ultrathin films with thicknesses from 2 to 27 nm.
- Optical properties were modeled using multilayer interference and parametric refractive index models.
- The method shows potential for imaging and determining material properties of semitransparent thin films.

## Abstract

In this paper, we demonstrate a novel optical characterization
method for ultrathin semitransparent and absorbing materials through
multispectral intensity and phase imaging. The method is based on
a lateral-shearing interferometric microscopy (LIM) technique, where
phase-shifting allows extraction of both the intensity and the phase
of transmitted optical fields. To demonstrate the performance in characterizing
semitransparent thin films, we fabricated and measured cupric oxide
(CuO) seeded gold ultrathin metal films (UTMFs) with mass-equivalent
thicknesses from 2 to 27 nm on fused silica substrates. The optical
properties were modeled using multilayer thin film interference and
a parametric model of their complex refractive indices. The UTMF samples
were imaged in the spectral range from 475 to 750 nm using the proposed
LIM technique, and the model parameters were fitted to the measured
data in order to determine the respective complex refractive indices
for varying thicknesses. Overall, by using the combined intensity
and phase not only for imaging and quality control but also for determining
the material properties, such as complex refractive indices, this
technique demonstrates a high potential for the characterization of
the optical properties, of (semi-) transparent thin films.